1. Field of the Invention
The present invention relates to the manufacture of foamed sheet material and pertains particularly to an apparatus and method for distributing a foamed fluid composition on a movable substrate to produce a foamed sheet material.
2. Discussion of the Prior Art
It is known to apply a viscous foamed fluid composition to a movable substrate and then, as necessary subsequently, to dry and cure the foamed composition. Such processes are used to produce foamed sheet materials, such as foam backed carpet and foam underlays for carpets. The foamed fluid composition may be a latex or a urethane. Previously such foamed compositions have been applied to the substrate and then distributed across the substrate by methods well known to the art using doctor blades or doctor rolls. It is desirable at times to provide a surface pattern on the foamed sheet material so produced. In the past a second step was necessary to produce this pattern since the doctor blades or rolls had smooth distribution edges or surfaces, thereby producing a foamed sheet material with a planar surface. To perform this second step, a variety of embossing techniques were developed, such as that taught in U.S. Pat. No. 3,210,447. In addition to being two-step processes requiring a high degree of control and coordination between the steps, all of these techniques had the added disadvantages of design inflexibility and high tooling cost in the embossing apparatus and wastage of the foamed composition where it was compressed by the embossed indentations.
An improved method and apparatus for producing patterned foam sheet materials were developed in U.K. Pat. No. 1,241,800, wherein the distribution and the pattern forming steps were combined. A series of doctor blades with lower edges having a variety of notches, cut-out parts, or protrusions were used to distribute the foamed composition and simultaneously produce a pattern of ridges and valleys on the surface of the foamed sheet material. A wide variety of patterns could be produced with tooling costs substantially lower than with embossing techniques and without wasting the foamed composition in embossed indentations. However, the specification provided no clear teaching on the mechanism used for moving the blades into and away from the distribution position nor on the methods used for mounting the blades. Additionally, there was no teaching on methods which could be used for substituting one or more blades for blades already mounted on the apparatus without stopping the process to make these substitutions nor was there any teaching on distribution means other than doctor blades.
The present invention is an improvement upon this prior art and seeks to overcome the limitations in its teachings. It is an object of the present invention to provide an improved apparatus and method for distributing a foamed fluid composition on a movable substrate in a one-step continuous operation producing a sequence of foamed sheet materials whose surfaces may be planar or variously patterned, wherein the distribution means and the pattern forming means are combined and may be either a doctor blade or a doctor roll and wherein the distribution means may be readily changed without interrupting the continuous process.